1. Field of the Invention
The present invention relates to an exposure apparatus and a method of device fabrication.
2. Description of the Related Art
There are available various types of methods of manufacturing a color filter such as a dyeing method, printing method, electrodeposition/electrolysis method, and pigment dispersion method. Among these methods, the pigment dispersion method has been the mainstream because of its manufacturing stability and simplicity. A photosensitive acrylic method as a typical pigment dispersion method forms a pattern by photolithography on a color resist containing an acryloid-based photosensitive resin and having both a coloring function and a photosensitive function.
A color resist is a negative resist. For this reason, irradiating the resist with exposure light will generate radicals contributing to a reaction and photopolymerize a polymer, thereby making it insoluble to a developer. Note however that the pigment components contained in the color resist easily absorb exposure light and the generated radicals are trapped in oxygen in air. This tends to hinder a photopolymerization reaction. In order to obtain predetermined pattern dimensions (or shape), therefore, it is necessary to increase the dose (exposure energy), leading to a decrease in throughput.
Under the circumstance, there has been proposed a technique of forming (applying) a film made of polyvinyl alcohol (oxygen shielding film which shields against oxygen) on a resist. Such a technique may cause a pattern defect due to the poor wettability of the oxygen shielding film on the resist. In addition, adding the step of forming an oxygen shielding film will increase the cost. Furthermore, it is not possible to control the oxygen concentration even by forming an oxygen shielding film. This reduces flexibility with respect to accuracy control on pattern dimensions when forming a fine pattern.
On the other hand, Japanese Patent Laid-Open No. H1-195445 has proposed a technique of exposing a resist in a low oxygen state upon blowing nitrogen (gas) against the resist without forming any oxygen shielding film made of polyvinyl alcohol on the resist. Japanese Patent Laid-Open No. S61-51150 has also proposed a technique of exposing a substrate separately in the first exposure step of exposing the substrate in an inert gas atmosphere and the second exposure step of exposing the substrate in an active gas atmosphere in order to obtain a high-resolution resist image.
According to the conventional technique, the hindrance of a photopolymerization reaction by oxygen is suppressed by setting different oxygen concentrations on a substrate (resist) in the first and second exposure steps, thereby obtaining predetermined pattern dimensions. In this case, if the illuminance of exposure light on a substrate decreases due to a decrease in the transmittance of an optical system or a decrease in the emission intensity of a light source, the photopolymerization reaction on the resist may change. If the photopolymerization reaction on the resist changes, the conventional technique of exposing a substrate in a plurality of steps may not obtain predetermined pattern dimensions. It is therefore conceivable to optimize pattern dimensions by increasing the dose. This will, however, decrease the throughput.